1. Field of the Invention
The invention relates to a substantially liquid, aqueous, rare earth oxide based composition for preserving the lustre of the smooth surfaces of objects needing to have such an appearance.
2. Technological Background
The invention applies more specifically, though not exclusively, to the preservation of surfaces of glazings of the so-called semi-reflective type, that is, glazings on which one of the surfaces is rendered partially reflective of luminous rays by being coated with a thin layer of metal compounds, such as metal oxides.
The thickness of the above-mentioned layer is generally between zero point three and one point two micrometers (0.3 and 1.2 .mu.m).
It will be noted that the composition of the invention can also be applied to the surfaces of objects made of natural materials as diverse as polyvinyl chloride, stainless steel, varnish paint, copper, and marble.
Whatever the case may be, semi-reflective type glazings have the characteristic of being sensitive to certain atmospheric agents which considerably alter the lustre of their partially reflective surface.
When thus altered, these glazings lose their transparency at the part of the luminous spectrum at which they are initially transparent, but still tend to become absorbent for a large part of the luminous spectrum, which tends to raise their temperature and goes contrary to the thermal insulation effects sought in the field of these semi-reflective glazings.
The lustre of the partially reflective surface of these glazings must therefore be regularly maintained, that is, cleared of the elements which alter it.
In the field of cleaning glazings, particularly in order to eliminate the potential build-up of silicone, it has long been known (GB-A-1.267.509) to use a composition consisting of a combination of at least one detergent agent and at least one metal oxide powder, such as a cerium oxide powder.
This type of composition is criticized for being especially subject to the phenomenon of syneresis and, moreover, for sensitizing the semi-reflective glazings to the action of the altering atmospheric agents.
Also, in the field of polishing optical surfaces, there are known polishing compositions such as that described in the patent application (GB-A-2.011.939).
Such polishing compositions contain cerium oxide particles whose diameter is between one and fifty microns, which gives them a highly abrasive quality and prevents their use for the preservation of glazings of the above-mentioned type.
The abrasive composition described in the patent application (EP-A-0.336.651) would also be unsuitable for the preservation of glazings of the above-mentioned type because it contains, in particular, abrasive particles whose diameter is between thirty and five hundred microns.